Transmembrane Transport

Question 1

What are the three major functions of cell membranes

Answer 1

1. separate the cell contents from the outside
2. separate the contents of different organelles from the rest of the cell
3. form a permeability barrier to many biologically important molecules

Question 2

cells need to take up various substances such as large uncharged polar molecules including

Answer 2

glucose and fructose

Question 3

cells need to take up various substances such as ions, give some examples

Answer 3

k+ mg2+ , basically any ion lols

Question 4

cells need to take up various substances such as charged polar molecules including

Answer 4

amino acids, atp, proteins, nucleic acids

Question 5

what is the typical composition of a cell membrane in terms of the amount of protein compared to the amount of lipid

Answer 5

50% protein, 50% lipid

Question 6

the membrane of a mitochondria has 75% protein and 25% lipid, why is this

Answer 6

because oxidative proteins are found throughout the membrane for respiration

Question 7

the membrane of myelin sheath is 25% protein and 75% lipid, why is this

Answer 7

because the nerve cells require insulation

Question 8

what component of the cell membrane is the key to the ‘selective permeability’ we describe cells as having

Answer 8

it is the protein component of the membrane that is key to the selective permeability to most physiologically important solutes. these are the gateways into cells

Question 9

membrane proteins have a wide variety of functions, label the following five proteins

Answer 9

channels, transpoters, connexins, receptors and enzymes

Question 10

what do membrane proteins that are channels do

Answer 10

they allow the ions to be transported across in order to maintain equilibrium

Question 11

give an example of protein channel

Answer 11

the CFTR protein channel

Question 12

what does the CFTR protein channel transport across

Answer 12

chloride ions

Question 13

what does cftr stand for

Answer 13

Cystic fibrosis transmembrane conductance regulator

Question 14

what do mutations in the CFTR protein channel result in

Answer 14

cystic fibrosis

Question 15

what do transporter proteins along the cell membrane do

Answer 15

transport substances such as amino acids, sugars and drugs up the concentration gradient

Question 16

what do connexins do

Answer 16

they interact with the cytoskeleton, extracellular matrix or other cells

Question 17

what do protein receptors along the cell membrane do

Answer 17

they are involved in endocytosis and or/transmission of signals across the membrane without movement of the ligand

Question 18

give an example of a protein transporter

Answer 18

ABCB1

Question 19

what does abcb1, the protein transporter do

Answer 19

it is a drug efflux pump, causes multidrug resistance

Question 20

give an example of a connexin/integrin membrane protein

Answer 20

Cx26

Question 21

where is Cx26 found

Answer 21

between cochlear cells

Question 22

what does Cx26 allow to happen

Answer 22

allows ion flow and so communication between cells

Question 23

a mutation in the gene of Cx26 results in what

Answer 23

congenital deafness

Question 24

congenital means?

Answer 24

present from birth

Question 25

what ion does the Cx26 connexin transport

Answer 25

k+ ions

Question 26

give an example of a protein receptor

Answer 26

FGFR3 + FGF

Question 27

if there is a mutation in the protein receptor FGFR3 + FGF, what disease can occur

Answer 27

achondroplasia

Question 28

what is achondroplasia

Answer 28

a cause of dwarfism

Question 29

give an example of an enzyme membrane protein

Answer 29

enzyme phospholipase c

Question 30

phospholipase c which is an example of an enzyme protein on the cell membrane converts phosphatidylinositol into which two substances

Answer 30

ip3 + DAG

Question 31

once phosphatidylinositol is converted to ip3 + DAG, what does the ip3 allow and what does the DAG allow

Answer 31

ip3 - releases Ca2+ ions from ER and DAG allows PKC activation

Question 32

how would you describe a channel protein

Answer 32

a continuous pore through a membrane

Question 33

explain how a channel pore can be selective

Answer 33

it may allow +ve ions through if negatively charged but not allow -ve ions through, or vice versa

Question 34

in what direction (in terms of concentration gradients) does a channel protein work

Answer 34

it only works down hill - solute moves down its electrochemical gradient to equilibrium

Question 35

is the bulk flow high or low in a channel protein

Answer 35

high bulk flow

Question 36

what type of movement occurs across channel proteins and passive transporters/carrier proteins

Answer 36

facilitated diffusion

Question 37

a carrier transporter/passive transporter can transport molecules that are too large or too polar from both sides of the membrane, how?

Answer 37

a passive transporter has specific solute binding sites alternately exposed on different sides of the membrane

Question 38

in what direction does a passive transporter/carrier protein work in terms of concentration

Answer 38

works down-hill, down the concentration gradient

Question 39

what type of flow can occur across a passive transporter

Answer 39

low capacity flow

Question 40

briefly describe passive transport in three key points

Answer 40

1. solute binding sites randomly exposed on either side of mem 2. solute binding induces a conformational change, exposing solute to other side of mem 3. net flux is dependent on the gradient, and only to equilibrium - obvs doesnt require energy

Question 41

where are solute binding sites present in active transport

Answer 41

high affinity solute binding site exposed to cytosol

Question 42

when a solute binds to an active transpoter, what does this induce

Answer 42

solute binding induces atp binding

Question 43

what is the net flux dependent on in an active transporter and in which direction can the solutes flow

Answer 43

net flux is dependent on atp (primary active pump) and can be uphill - against the conc gradient

Question 44

*explain this diagram in terms of the electrochemical gradient

Answer 44

electrochemical gradient with no membrane potential

Question 45

*explain this diagram in terms of the electrochemical gradient

Answer 45

electrochemical gradient with membrane potential negative inside

Question 46

*explain this diagram in terms of the electrochemical gradient

Answer 46

electrochemical gradient with membrane potential positive inside

Question 47

which of the three electrochemical gradients is most pertinent to the human plasma membrane

Answer 47

electrochemical gradient with membrane potential negative inside

Question 48

what creates a powerful electrochemical gradient for Na+ ions

Answer 48

the -ve charge on the inner leaflet phosphatidyl-serine combined with the efflux of sodium ions by the Na+/K+ ATPase pump generates a powerful electrochemical gradient for Na+

Question 49

some transporters use ATP to provide the energy for solutes to move against the concentration gradient, what other method can generate the energy to pump against the concentration gradient

Answer 49

transport can be driven using the energy from ion gradients - coupled transport

Question 50

what is coupled transport

Answer 50

coupling of the binding of both the transported solute and the co-transported solute

Question 51

what provides the energy to transport against the concentration gradient in coupled transport

Answer 51

the free energy released as the co-transported ion moves down its electrochemical gradient can drive the solute up its electrochemical gradient

Question 52

what is a ion gradient generated by

Answer 52

an atp driven pump

Question 53

why is coupled transport referred to as secondary active transport

Answer 53

because the ion gradient is generated by an ATP driven pump, so this is secondary active transport

Question 54

what is a symporter

Answer 54

symporters transport solutes in the same direction

Question 55

what is an antiporter

Answer 55

antiporters transport solutes in the opposite direction

Question 56

in a primary active transporter, uphill solute translocation is possible if coupled to what

Answer 56

ATP hydrolysis

Question 57

in a secondary active transporter, uphill solute translocation is possible if coupled to what

Answer 57

if coupled to the downhill movement of another solute

Question 58

give an example of a primary active transporter

Answer 58

SERCA - the sacroplasmic/endoplasmic reticulum Ca2+ P-type ATPase

Question 59

give an example of a secondary active transporter

Answer 59

SGLT1 the sodium/glucose linked transporter

Question 60

where is the sodium glucose linked transporter found

Answer 60

in the intestinal epithelium

Question 61

List the three transporters involved in glucose uptake in the epithelium lining the small intestine

Answer 61

1. sglt1 symporter 2. passive transporter 3. na+/k+ ATPase

Question 62

what is the role of the SGLT1 symporter in glucose uptake

Answer 62

the sglt1 symporter is a na+ driven symporter. glucose is transporter in after the entrance of na+.

Question 63

what type of active transport occurs at the SGLT1 symporter

Answer 63

secondary active transport

Question 64

what is the role of the proteins present at the basal domain in epithelial cells of the small intestine

Answer 64

glut2 facilitated diffusion - the downhill transport of glucose

Question 65

what occurs at the Na+/k+ pump in the epithelial cells

Answer 65

keeps cellular na+ low by pumping Na+ out into the extracellular fluid

Question 66

what type of transporter is the Na+/k+ atpase pump

Answer 66

a primary active transporter

Question 67

what is progressive familial intrahepatic cholestasis

Answer 67

Progressive familial intrahepatic cholestasis (PFIC) is a disorder that causes progressive liver disease, which typically leads to liver failure

Question 68

genetics has identified mutations in transporters resulting in progressive familial intrahepatic cholestasis, list the three transports which may have mutations in them

Answer 68

Atp8b1 - transports phosphatidyl-serine abcb4- transports phosphatidyl-choline abcb11 - transports bile salts

Question 69

give an example of a particle that is internalised by receptor mediated endocytosis

Answer 69

LDL - cholesterol rich low density lipoprotein particles

Question 70

once the ldl has bound to the ldl binding site of the dl receptor protein on the plasma membrane, what prevents the ldl partciels from entering the cells

Answer 70

the ldl particles are prevented from entering the cells as there is a clathrin coated pit prsent

Question 71

some people have a genetic mutation resulting in the clathrin pit not being present, what does this result in

Answer 71

hypercholesterolaemia, where the clathrin interaction domain is deleted

Question 72

what can hypercholesterolaemia result in

Answer 72

a greater risk of atherosclerosis and chd

Question 73

what is cftr and where is it present

Answer 73

cftr stands for cystic fibrosis transmembrane regulator, it is a cl- channel and is present on the plasma membrane of epithelial cells of the lung, intestine and pancreas

Question 74

once cl- is transported across the cftr channel protein, what does this induce the flow of

Answer 74

once cl- is transported across, this induces the flow of na+ and water

Question 75

when na+ and water is transported out of the plasma membrane, what does this reduce

Answer 75

reduces the viscosity of the surface mucous

Question 76

what happens when the cftr protein is mutated

Answer 76

results in cystic fibrosis. viscous mucous reduces the function of the epithelial cells, causing chronic infection, inflammation and fibrosis

Question 77

what is fibrosis

Answer 77

the thickening and scarring of connective tissue

Question 78

mutations of the cftr protein are usually of what type

Answer 78

autosomal recessive

Question 79

there are usually two types of mutation of cftr, what are these

Answer 79

they either impair the opening of the channel or impair folding of the channel in the er

Question 80

which mutation is more common, the impaired opening or the impaired folding

Answer 80

the impaired folding is more common,

Question 81

impairment of the opening of the channel is a result of a genetic mutation in

Answer 81

g551d

Question 82

impairment of the folding of the channel is a result of the genetic mutation in

Answer 82

f508

Question 83

focusing on the treatment of cystic fibrosis, what are correctors effective against

Answer 83

they are effective against deltaf508 which impairs the folding of the channel in the er

Question 84

name a corrector used in the treatment of cystic fibrosis

Answer 84

suberoylanilide hydroxamic acid (saha)

Question 85

how does suberoylanilide hydroxamic acid work

Answer 85

switches on different folding chaperones which allow f508 to fold

Question 86

what are potentiators effective against

Answer 86

g551d which impairs the opening of the channel

Question 87

give an example of a potentiator used in the treatment of cystic fibrosis

Answer 87

ivacaftor

Question 88

how does ivacaftor work

Answer 88

works by binding directly to the channel and increasing its ability to open

Question 89

gene therapy currently has ongoing trials, it is likely to be an effective treatment for what part of the body

Answer 89

the lungs